CHRISTINA CAMPBELL CAN easily list the ways that being single costs her financially: When she was self-employed, she paid more for her individual health insurance plan than if she were part of a couple, or if she could have piggy-backed on a spouse's plan. She also notes that her retirement savings options are more limited than they are for couples, who can contribute to each other's IRAs. "If I were to suddenly become unemployed, my retirement savings would certainly suffer in a way that they wouldn't if I had a husband," says Campbell, 38, who lives in Centreville, Va.

[Read: 10 Smart Ways to Improve Your Budget.]

Campbell, one of the voices behind the pro-single website onely.org, points to a variety of other employer policies that give preferences to couples, as well. Spouses often get bereavement leave for each other's close family members, while Campbell was unable to take leave for her uncle's funeral. She also couldn't add beneficiaries outside her nuclear family to her long-term care insurance without taking out a separate policy.

As Campbell found from first-hand experience, single people often face unique financial stresses that can take a heavy toll, especially as they approach retirement. A new report from the MetLife Mature Market Institute and the Society of Actuaries found that single people have more financial stresses than couples do, and single women in particular say they have a harder time saving for retirement than married couples do.

Singles, in fact, reported the lowest income levels ($32,000, on average), asset levels ($110,000), and the homeownership rates (43 percent) compared to other family structures. Just 17 percent said they believed they were on track to reach their retirement savings goals, and one-fifth had not yet started putting away money for retirement. Most single respondents said they worry about affording their living expenses and maintaining their standard of living in retirement.

Many of those financial stresses originate from having only one income to rely on, says MetLife Mature Market Institute's Sandra Timmermann. "Single people are more vulnerable than the couples who have double earnings," she says, adding that that's the case whether they have children or not. Single people also tend to earn less than married couples, she points out, and on average, they have lower education levels.

[Read: The High Price of Living Alone.]

The study, which surveyed adults between ages 45 and 80, also found that couples were more likely than singles to have taken steps to pay off debt, met with a financial adviser, and invested for retirement. "It almost seems that when you have a partner and somebody to work with, there is more of an incentive to do planning," says Timmermann.

The study comes at a time of peak interest in singles, given the country's shifting demographics. According to the Census Bureau, the number of single-person households has grown to 31 million, up 15 percent between 2000 and 2010. Meanwhile, husband-wife households are on the decline, now making up less than half of total households. If singles aren't financially secure, then a large chunk of the country isn't financially secure.

Still, despite the alarming findings, some singles say they're better off than they would be in a couple, especially if their partner was less financially responsible. "It's far easier for me to save for retirement, because my money is my own and I can spend it how I want to," says Eleanore Wells, a singles expert and author of The Spinsterlicious Life.

Wells acknowledges that a second income from a partner might allow her to live in a "bigger, fancier apartment," the travel industry often offers couples' discounts, and wireless companies often give discounts for family plans, but otherwise, being single doesn't impose too much of a financial burden. "I think the opposite is true. Some of my friends are married to delightful guys but they're terrible money managers … What I like about being single is that all my decisions are my own," she says.

[Read: The Cost of Getting Married.]

For singles looking to combat financial stress, financial experts and singles themselves suggest the following:

Build your support network. In addition to socking away money in her 401(k) and taking out long-term care and disability insurance, Wells says, "I'm making sure I'm surrounded by friends and family who care about me, so when someone needs to take care of me, I'll have people to choose from," she says.

Take savvy steps that apply to singles and couples alike. Saving as much as possible, cutting out frivolous expenses, and planning for retirement early—all of these steps are useful regardless of relationship status.

Get a head start on retirement. MetLife notes that single people are highly concerned about retirement but are less likely to have purchased retirement-related financial products than couples. The company urges singles to save for retirement early, even if it's in small increments. Timmermann adds that women in particular should focus on retirement savings as soon as possible, since women live longer than men.

Take advantage of employee benefits. While some policies might benefit couples more than singles, as Campbell found, others are equally useful to all eligible employees: 401(k) accounts for retirement savings, for example, and disability insurance. "So many people don't realize that if they don't put the maximum into their 401(k), they won't get the full employer match," says Timmermann.

Fight for your rights. "Why should singles adapt their behavior to a system that discriminates against them?" asks Campbell. Instead, she says, "We should be fighting against the institutionalization of the married-is-better-than-single trope." She suggests challenging gym policies that offer cheaper policies to couples, for example.

Take care of dependents. For single parents, arranging wills, trusts, and guardianships for children is especially important. This might not directly help the parent's financial security, but it will have a big impact on children in the unlikely event of the parent's unexpected death.

But take care of yourself first. Timmermann points out that single parents are often taking care of their own children, including adult ones, while simultaneously caring for their parents. "Your temptation is to help them and help your grandchildren, but that could be detrimental to yourself," she says.

In other words, singles might have to work a little harder to look out for their own financial security.